共查询到20条相似文献，搜索用时 171 毫秒
1.
George L. Withbroe 《Solar physics》2009,257(1):71-81
The daily images and magnetograms acquired by MDI are a rich source of information about the contributions of different types
of solar regions to variations in the total solar irradiance (TSI). These data have been used to determine the temporal variation
of the MDI irradiance, the mean intensity of the solar disk in the continuum at 676.8 nm. The short-term (days to weeks) variations
of the MDI irradiance and TSI are in excellent agreement with rms differences of 0.011%. This indicates that MDI irradiance
is an excellent proxy for short-term variations of TSI from the competing irradiance contributions of regions causing irradiance
increases, such as plages and bright network, and regions causing irradiance decreases, such as sunspots. However, the long-term
or solar cycle variation of the MDI proxy and TSI differ over the 11-year period studied. The results indicate that the primary
sources of the long-term (several months or more) variations in TSI are regions with magnetic fields between about 80 and
600 G. The results also suggest that the difference in the long-term variations of the MDI proxy and TSI is due to a component
of TSI associated with sectors of the solar spectrum where the contrast in intensity between plages and the quiet Sun is enhanced
(e.g., the UV) compared to the MDI proxy. This is evidence that the long-term variation of TSI is due primarily to solar cycle
variations of the irradiance from these portions of solar spectrum, a finding consistent with modeling calculations indicating
that approximately 60% of the change in TSI between solar minimum and maximum is produced by the UV part of the spectrum shortward
of 400 nm (Solanki and Krivova, Space Sci. Rev. 125, 53, 2006). 相似文献
2.
Judit M. Pap Richard C. Willson Claus Fröhlich Richard F. Donnelly Larry Puga 《Solar physics》1994,152(1):13-21
For more than a decade total solar irradiance has been monitored simultaneously from space by different satellites. The detection of total solar irradiance variations by satellite-based experiments during the past decade and a half has stimulated modeling efforts to help identify their causes and to provide estimates of irradiance data, using proxy indicators of solar activity, for time intervals when no satellite observations exist. In this paper total solar irradiance observed by the Nimbus-7/ERB, SMM/ACRIM I, and UARS/ACRIM II radiometers is modeled with the Photometric Sunspot Index and the Mg II core-to-wing ratio. Since the formation of the Mg II line is very similar to that of the Ca II K line, the Mg core-to-wing ratio, derived from the irradiance observations of the Nimbus-7 and NOAA9 satellites, is used as a proxy for the bright magnetic elements. It is shown that the observed changes in total solar irradiance are underestimated by the proxy models at the time of maximum and during the beginning of the declining portion of solar cycle 22 similar to behavior just before the maximum of solar cycle 21. This disagreement between total irradiance observations and their model estimates is indicative of the fact that the underlying physical mechanism of the changes observed in the solar radiative output is not well-understood. Furthermore, the uncertainties in the proxy data used for irradiance modeling and the resulting limitation of the models should be taken into account, especially when the irradiance models are used for climatic studies. 相似文献
3.
Regular monitoring of solar irradiance has been carried out since 1978 to show that solar total and spectral irradiance varies at different time scales. Whereas variations on time scales of minutes to hours are due to solar oscillations and granulation, variations on longer time scales are driven by the evolution of the solar surface magnetic field. Here the most recent advances in modelling of solar irradiance variations on time scales longer than a day are briefly reviewed. 相似文献
4.
太阳总辐照是指在地球大气层顶接收到的太阳总辐射照度,也叫"太阳常数",但它实际上并非常数。太阳总辐照随波长的分布即为太阳分光辐照。太阳辐照变化的研究,对理解太阳表面及内部活动的物理过程、机制,研究地球大气、日地关系,解决人类面临的全球气候变暖的挑战等,都具有重要意义。首先简单介绍了太阳辐照,回顾了太阳辐照的空间观测;接着介绍了观测数据的并合,以及对合成数据的一些研究;然后讨论了太阳辐照变化的原因,简述了太阳总辐照的重构及其在气候研究上的一些应用,并进行必要的评论;最后对未来的研究方向提出了一些看法。 相似文献
5.
6.
Variations of total solar irradiance, 10.7 cm radio emission, the Hei 10830 Ú equivalent width and the solar magnetic field flux measured for the entire Sun are compared with variations of the energy index of the global solar magnetic field and the index of the effective solar multipole for years 1979–1992. It is shown that photospheric radiation and that generated in the upper chromosphere and corona display different relationships with the global magnetic field of the Sun, and that interaction between the magnetic field and the solar irradiance is much more complicated than the traditional blocking effect. 相似文献
7.
Although solar ultraviolet (UV) irradiance measurements have been made regularly from satellite instruments for almost 20 years, only one complete solar cycle minimum has been observed during this period. Solar activity is currently moving through the minimum phase between cycles 22 and 23, so it is of interest to compare recent data taken from the NOAA-9 SBUV/2 instrument with data taken by the same instrument during the previous solar minimum in 1985–1986. NOAA-9 SBUV/2 is the first instrument to make continuous solar UV measurements for a complete solar cycle. Direct irradiance measurements (e.g., 205 nm) from NOAA-9 are currently useful for examining short-term variations, but have not been corrected for long-term instrument sensitivity changes. We use the Mgii proxy index to illustrate variability on solar cycle time scales, and to provide complementary information on short-term variability. Comparisons with contemporaneous data from Nimbus-7 SBUV (1985–1986) and UARS SUSIM (1994–1995) are used to validate the results obtained from the NOAA-9 data. Current short-term UV activity differs from the cycle 21–22 minimum. Continuous 13-day periodicity was observed from September 1994 to March 1995, a condition which has only been seen previously for shorter intervals during rising or maximum activity levels. The 205 nm irradiance and Mgii index are expected to track very closely on short time scales, but show differences in behavior during the minimum between cycles 22 and 23. 相似文献
8.
Variations of solar total and spectral irradiance are prime solar quantities purported to have an influence on the Earth’s
climate. Quantitative estimates of irradiance over as long a time as possible are needed to judge their effectiveness in forcing
the climate. In order to do this reliably, first the measured record must be reproduced and a feeling for the physics underlying
the irradiance variations must be developed. With the help of this knowledge combined with the available proxy data, reconstructions
of irradiance in the past, generally since the Maunder minimum, are attempted. Here a brief introduction to some of the irradiance
reconstruction work aiming at irradiance on time scales of days to the solar cycle is given, followed by a brief and incomplete
overview of the longer-term reconstructions. 相似文献
9.
Owens Mathew Lang Matthew Barnard Luke Riley Pete Ben-Nun Michal Scott Chris J. Lockwood Mike Reiss Martin A. Arge Charles N. Gonzi Siegfried 《Solar physics》2020,295(3):1-15
Solar radiation variability spans a wide range in time, ranging from seconds to decadal and longer. The nearly 40 years of measurements of solar irradiance from space established that the total solar irradiance varies by \(\approx 0.1\%\) in phase with the Sun’s magnetic cycle. Specific intervals of the solar spectrum, e.g., ultraviolet (UV), vary by orders of magnitude more. These variations can affect the Earth’s climate in a complex non-linear way. Specifically, some of the processes of interaction between solar UV radiation and the Earth’s atmosphere involve threshold processes and do not require a detailed reconstruction of the solar spectrum. For this reason a spectral UV index based on the (FUV-MUV) color has been recently introduced. This color is calculated using SORCE SOLSTICE integrated fluxes in the FUV and MUV bands. We present in this work the reconstructions of the solar (FUV-MUV) color and Ca ii K and Mg ii indices, from 1749–2015, using a semi-empirical approach based on the reconstruction of the area coverage of different solar magnetic features, i.e., sunspot, faculae and network. We remark that our results are in noteworthy agreement with latest solar UV proxy reconstructions that exploit more sophisticated techniques requiring historical full-disk observations. This makes us confident that our technique can represent an alternative approach which can complement classical solar reconstruction efforts. Moreover, this technique, based on broad-band observations, can be utilized to estimate the activity on Sun-like stars, that cannot be resolved spatially, hosting extra-solar planetary systems.
相似文献10.
G. Houdek W.J. Chaplin T. Appourchaux J. Christensen-Dalsgaard W. Däppen Y. Elsworth D.O. Gough G.R. Isaak R. New M.C. Rabello-Soares 《Monthly notices of the Royal Astronomical Society》2001,327(2):483-487
Measurements of both solar irradiance and p-mode oscillation frequencies indicate that the structure of the Sun changes with the solar cycle. Balmforth, Gough & Merryfield investigated the effect of symmetrical thermal disturbances on the solar structure and the resulting pulsation frequency changes. They concluded that thermal perturbations alone cannot account for the variations in both irradiance and p-mode frequencies, and that the presence of a magnetic field affecting acoustical propagation is the most likely explanation of the frequency change, in the manner suggested earlier by Gough & Thompson and by Goldreich et al. Numerical simulations of Boussinesq convection in a magnetic field have shown that at high Rayleigh number the magnetic field can modify the preferred horizontal length scale of the convective flow.
Here, we investigate the effect of changing the horizontal length scale of convective eddies on the linewidths of the acoustic resonant mode peaks observed in helioseismic power spectra. The turbulent fluxes in these model computations are obtained from a time-dependent, non-local generalization of the mixing-length formalism. The modelled variations are compared with p-mode linewidth changes revealed by the analysis of helioseismic data collected by the Birmingham Solar-Oscillations Network (BiSON); these low-degree (low- l ) observations cover the complete falling phase of solar activity cycle 22. The results are also discussed in the light of observations of solar-cycle variations of the horizontal size of granules and with results from 2D simulations by Steffen of convective granules. 相似文献
Here, we investigate the effect of changing the horizontal length scale of convective eddies on the linewidths of the acoustic resonant mode peaks observed in helioseismic power spectra. The turbulent fluxes in these model computations are obtained from a time-dependent, non-local generalization of the mixing-length formalism. The modelled variations are compared with p-mode linewidth changes revealed by the analysis of helioseismic data collected by the Birmingham Solar-Oscillations Network (BiSON); these low-degree (low- l ) observations cover the complete falling phase of solar activity cycle 22. The results are also discussed in the light of observations of solar-cycle variations of the horizontal size of granules and with results from 2D simulations by Steffen of convective granules. 相似文献
11.
Global changes of the solar activity can be expressed by the coronal index that is based upon the total irradiance of the coronal 530.3 nm green line from observations at five stations. Daily mean values of the coronal index of solar activity and other well-correlated solar indices are analyzed for the period 1966–1998 covering over three solar cycles. The significant correlation of this index with the sunspot number and the solar flare index have led to an analytical expression which can reproduce the coronal index of solar activity as a function of these parameters. This expression explains well the existence of the two maxima during the solar cycles taking into account the evolution of the magnetic field that can be expressed by some sinusoidal terms during solar maxima and minima. The accuracy between observed and calculated values of the coronal index on a daily basis reaches the value of 71%. It is concluded that the representative character of the coronal index is preserved even when using daily data and can therefore allow us to study long-term, intermediate and short-term variations for the Sun as a star, in association with different periodical solar–terrestrial phenomena useful for space weather studies. 相似文献
12.
Knowledge of solar spectral irradiance (SSI) is important in determining the impact of solar variability on climate. Observations of UV SSI have been made by the Solar Ultraviolet Spectral Irradiance Monitor (SUSIM) on the Upper Atmosphere Research Satellite (UARS), the Solar-Stellar Irradiance Comparison Experiment (SOLSTICE), and the Solar Irradiance Monitor (SIM), both on the Solar Radiation and Climate Experiment (SORCE) satellite. Measurements by SUSIM and SORCE overlapped from 2003 to 2005. SUSIM and SORCE observations represent ～?20 years of absolute UV SSI. Unfortunately, significant differences exist between these two data sets. In particular, changes in SORCE UV SSI measurements, gathered at moderate and minimum solar activity, are a factor of two greater than the changes in SUSIM observations over the entire solar cycle. In addition, SORCE UV SSI have a substantially different relationship with the Mg ii index than did earlier UV SSI observations. Acceptance of these new SORCE results impose significant changes on our understanding of UV SSI variation. Alternatively, these differences in UV SSI observations indicate that some or all of these instruments have changes in instrument responsivity that are not fully accounted for by the current calibration. In this study, we compare UV SSI changes from SUSIM with those from SIM and SOLSTICE. The primary results are that (1) long-term observations by SUSIM and SORCE generally do not agree during the overlap period (2003?–?2005), (2) SUSIM observations during this overlap period are consistent with an SSI model based on Mg ii and early SUSIM SSI, and (3) when comparing the spectral irradiance for times of similar solar activity on either side of solar minimum, SUSIM observations show slight differences while the SORCE observations show variations that increase with time between spectra. Based on this work, we conclude that the instrument responsivity for SOLSTICE and SIM need to be reevaluated before these results can be used for climate-modeling studies. 相似文献
13.
Ann T. Mecherikunnel 《Solar physics》1998,177(1-2):11-23
Simultaneous solar total irradiance observations performed by absolute radiometers on board satellites during the quiet-Sun period between solar cycles 21 and 22 (1985–1987), are analyzed to determine the solar total irradiance at 1 AU for the solar minimum. During the quiet-Sun period the total solar irradiance, UV irradiance, and the various solar activity indices show very little fluctuation. However, the absolute value of the solar total irradiance derived from the observations differ within the accuracy of the radiometers used in the measurements. Therefore, the question often arises about a reference value of the solar total irradiance for use in climate models and for computation of geophysical, and atmospheric parameters. This research is conducted as a part of the Solar Electromagnetic Radiation Study for Solar Cycle 22 (SOLERS22). On the basis of the study we recommended a reference value of 1367.0 ± 0.04 W m-2 for the solar total irradiance at 1 AU for a truly quiet Sun. We also find that the total solar irradiance data for the quiet-Sun period reveals strong short-term irradiance variations. 相似文献
14.
Steven Dewitte Dominique Crommelynck Sabri Mekaoui Alexandre Joukoff 《Solar physics》2004,224(1-2):209-216
A possible long-term trend of the total solar irradiance could be a natural cause for climate variations on Earth. Measurement
of the total solar irradiance with space radiometers started in 1978. We present a new total solar irradiance composite, with
an uncertainty of ± 0.35 W m−2. From the minimum in 1995 to the maximum in 2002 the total solar irradiance increased by 1.6 W m−2. In between the minima of 1987 and 1995 the total solar irradiance increased by 0.15 W m−2. 相似文献
15.
G. Feulner 《Solar physics》2013,282(2):615-627
The Mauna Loa Observatory record of direct-beam solar irradiance measurements for the years 1958?–?2010 is analysed to investigate the variation of clear-sky terrestrial insolation with solar activity over more than four solar cycles. The raw irradiance data exhibit a marked seasonal cycle, extended periods of lower irradiance due to emissions of volcanic aerosols, and a long-term decrease in atmospheric transmission independent of solar activity. After correcting for these effects, it is found that clear-sky terrestrial irradiance typically varies by ≈?0.2±0.1 % over the course of the solar cycle, a change of the same order of magnitude as the variations of the total solar irradiance above the atmosphere. An investigation of changes in the clear-sky atmospheric transmission fails to find a significant trend with sunspot number. Hence there is no evidence for a yet unknown effect amplifying variations of clear-sky irradiance with solar activity. 相似文献
16.
Electromagnetic radiation from the Sun is Earths primary energy source. Space-based radiometric measurements in the past two decades have begun to establish the nature, magnitude and origins of its variability. An 11-year cycle with peak-to-peak amplitude of order 0.1 % is now well established in recent total solar irradiance observations, as are larger variations of order 0.2 % associated with the Suns 27-day rotation period. The ultraviolet, visible and infrared spectral regions all participate in these variations, with larger changes at shorter wavelengths. Linkages of solar radiative output variations with solar magnetism are clearly identified. Active regions alter the local radiance, and their wavelength-dependent contrasts relative to the quiet Sun control the relative spectrum of irradiance variability. Solar radiative output also responds to sub-surface convection and to eruptive events on the Sun. On the shortest time scales, total irradiance exhibits five minute fluctuations of amplitude
%, and can increase to as much as 0.015 % during the very largest solar flares. Unknown is whether multi-decadal changes in solar activity produce longer-term irradiance variations larger than observed thus far in the contemporary epoch. Empirical associations with solar activity proxies suggest reduced total solar irradiance during the anomalously low activity in the seventeenth century Maunder Minimum relative to the present. Uncertainties in understanding the physical relationships between direct magnetic modulation of solar radiative output and heliospheric modulation of cosmogenic proxies preclude definitive historical irradiance estimates, as yet.Received: 26 August 2004, Published online: 16 November 2004
Correspondence to: Claus Fröhlich 相似文献
17.
H. Mavromichalaki 《Earth, Moon, and Planets》1989,47(1):61-72
The diurnal anisotropy of cosmic-ray intensity observed over the period 1970–1977 has been analysed using neutron-monitor data of the Athens and Deep River stations. Our results indicate that the time of the maximum of diurnal variation shows a remarkable systematic shift towards earlier hours than normally beginning in 1971. This phase shift continued until 1976, the solar activity minimum, except for a sudden shift to a later hour for one year, in 1974, the secondary maximum of solar activity.This behavior of the diurnal time of maximum has been shown to be consistent with the convective- diffusive mechanism which relates the solar diurnal anisotropy of cosmic-rays to the dynamics of the solar wind and of the interplanetary magnetic field. Once again we have confirmed the field-aligned direction of the diffusive vector independently of the interplanetary magnetic field polarity. It is also noteworthy that the diurnal phase may follow in time the variations of the size of the polar coronal holes. All these are in agreement with the drift motions of cosmic-ray particles in the interplanetarty magnetic field during this time period. 相似文献
18.
Analyses based on irradiance observations from space within the last one and a half decades have discovered variations in the entire solar spectrum and at UV wavelengths on time scales of minutes to decades. In this paper we analyze the distribution of the measuring uncertainties and daily fluctuations in total solar irradiance measured by the Nimbus-7/ERB and SMM/ACRIM I radiometers as a function of solar cycle. Changes in solar total irradiance and its surrogates shorter than the solar rotation have also been considered as noise and have been removed from the data. Our results show that the noise (both instrumental and solar noise) changes as a function of the solar cycle, being higher during high solar activity conditions. The analysis of the scatter plot diagrams between the data and their standard deviation, the so-called dispersion diagrams, provides a useful tool to estimate and predict the time of solar maximum and minimum activity conditions.Deceased on October 13, 1994. 相似文献
19.
A. V. Mordvinov 《Solar physics》1996,163(2):309-317
A new numerical technique is applied to study long-term variations of total solar irradiance. The background solar flux is estimated not from, e.g., a running mean but as the mode on a moving short time interval. Statistical properties of short-term variations with respect to the running mode are studied. The probability distribution function describing the data from Nimbus-7 is asymmetric and departs from a Gaussian.The ratio of time-integrated short-term negative and positive deviations shows that the energy re-radiated from faculae makes up about 40% of the energy blocked by sunspots. The amplitude and phase relations are studied between deviations which decrease and increase the irradiance. They characterize the mechanism of energy transformation with frequency. The cross-covariance analysis reveals that some parts of the energy blocked by sunspots come to the surface of the Sun after long delays. 相似文献
20.
Magnetic fields give rise to distinctive features in different solar atmospheric regimes. To study this, time variations of
the flare index, sunspot number and sunspot area, each index arising from different physical conditions, were compared with
the solar composite irradiance throughout cycle 23. Rieger-type periodicities in these time series were calculated using Fourier
and wavelet transforms (WTs). The peaks of the wavelet power of these periodicities appeared between the years 1999 and 2002.
We found that the solar irradiance oscillations are less significant than those in the other indices during this cycle. The
irradiance shows non-periodic fluctuations during this time interval. The peaks of the flare index, sunspot number and sunspot
total area were seen around 2000.4, 1999.9 and 2001.0, respectively. These periodicities appeared intermittently and were
not simultaneous in different solar activity indices during the three years of the maximum phase of solar cycle 23. 相似文献